Institute of Electrical and Electronics Engineers (IEEE) 802.11 is a set of physical and media access control (MAC) specifications for implementing wireless local area network (WLAN) communications between a set of network devices referred to as stations and/or access points. These specifications provide the basis for wireless network products using the Wi-Fi brand managed and defined by the Wi-Fi Alliance. The specifications define the use of the 2.400-2.500 GHz as well as the 4.915-5.825 GHz bands. These spectrum bands are commonly referred to as the 2.4 GHz and 5 GHz bands. Each spectrum is subdivided into channels with a center frequency and bandwidth. The 2.4 GHz band is divided into 14 channels spaced 5 MHz apart, though some countries regulate the availability of these channels. The 5 GHz band is more heavily regulated than the 2.4 GHz band and the spacing of channels varies across the spectrum with a minimum of a 5 MHs spacing dependent on the regulations of the respective country or territory.
Communication on any given channel of either the 2.4 GHz or the 5 GHz band between network elements of the WLAN utilizes the clear channel assessment (CCA) protocol. CCA is defined in the IEEE 802.11 standard as part of the Physical Medium Dependent (PMD) and Physical Layer Convergence Protocol (PLCP) layer. Clear Channel Assessment is composed of two related functions, carrier sense (CS) and energy detection (ED). The CCA protocol is implemented in the physical layer (PHY) of a network device and determines the current state of use of the wireless medium (WM) (i.e., a 2.4 GHz or 5 GHz band), such that a network device (e.g., a station) will access a channel of the WM only when the WM becomes idle.
The conventional CCA rule mechanism defined in IEEE 802.11 defines the primary channel to be busy, if one of the conditions listed in the Table I is met, otherwise the primary channel is considered to be idle. If the primary channel is idle, the PHY will check the secondary channels.
TABLE IOperating Channel WidthConditions20 MHz, 40 MHz, 80 MHz, The start of a 20 MHz NON_HT PPDU in the160 MHz or 80 + 80 MHzprimary 20 MHz channel as defined in18.3.10.6 (CCA requirements)40 MHz, 80 MHz, 160 MHz The start of a 40 MHz non-HT duplicate oror 80 + 80 MHzVHT PPDU in the primary 40 MHz channel ator above −79 dBm,The start of an HT PPDU under theconditions defined in 20.3.21.5 (CCAsensitivity)80 MHz, 160 MHz or The start of an 80 MHz non-HT duplicate or80 + 80 MHzVHT PPDU in the primary 80 MHz channelat or above −76 dBm60 MHz or 80 + 80 MHzThe start of a 160 MHz or 80 + 80 MHz non-HT duplicate or VHT PPDU at or above −73dBm